Optical glasses with improved varying partial dispersion in the optical positional range of lanthanum crown glasses and lanthanum flint glasses

ABSTRACT

Optical, fluorine containing barium borosilicate glasses having an improved varying partial dispersion in the optical positional range of lanthanum crown and lanthanum flint glasses wherein the ratio of SiO 2  with respect to SiO 2  and B 2  O 3  is at least 0.62 and the content of fluorine in said glass is between 2 and 7 grams per 100 cc of said glass.

This is a continuation of application Ser. No. 402,805, filed Oct. 2, 1973, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a novel class of optical glasses, and more particularly, to such glasses which exhibit good stability with respect to changes in climatic conditions, low staining susceptibility and can be ground, polished and pressed like ordinary silicate glasses. These glasses have the same optical position as lanthanum crown glasses (LaC) and lanthanum flint glasses (LaF), but exhibit a higher partial dispersion P_(g),F than prior glasses.

Normal commercial glasses, in the optical positional range of the LaC and LaF glasses, have a partial dispersion P_(g),F = (n_(g) - n_(F))/n_(F) - n_(C)) which is considerably reduced, by comparison, with the normal partial dispersion, as calculated from the Abbe equation

    P.sub.g,F = 0.6438 - 0.001682v.sub.d

and set forth, for example, in the Jenaer Glaswerk Schott & Gen. catalogue for optical glass no. 3050/1966/II 5.

Prior art glasses within the optical positional range of LaC and LaF glasses are characterized by the passage of a straight line through each of the following limiting values (as illustrated in FIG. 1):

    ______________________________________                                         n.sub.d = 1.642                                                                          v.sub.d = 58.0 to n.sub.d = 1.699                                                                 v.sub.d = 46.0                                    n.sub.d = 1.642                                                                          v.sub.d = 58.0 to n.sub.d = 1.652                                                                 v.sub.d = 58.5                                    n.sub.d = 1.652                                                                          v.sub.d = 58.5 to n.sub.d = 1.702                                                                 v.sub.d = 54.6                                    n.sub.d = 1.702                                                                          v.sub.d = 54.6 to n.sub.d = 1.742                                                                 v.sub.d = 44.0                                    n.sub.d = 1.742                                                                          v.sub.d = 44.0 to n.sub.d = 1.699                                                                 v.sub.d = 46.0                                    ______________________________________                                    

Each of these prior art glasses exhibit particularly low P_(g),F values.

Glasses having the lowest P_(g),F values and most extreme optical positions (e.g. n_(d) =1.697; v_(d) =55.4) consist essentially of B₂ O₃, CaO, La₂ O₃, ZrO₂ and less than 10 percent by weight of SiO₂. In addition to these ingredients, these glasses can also contain MgO, SrO, PbO, ZnO, CdO, TiO₂, Al₂ O₃, Nb₂ O₅, and WO₃ for varying the n_(d) and v_(d) values and for improving the crystallization stability and chemical resistivity of the glasses.

In prior art glasses, when the SiO₂ content was raised to above 10 percent by weight, with a corresponding reduction in the amount of B₂ O₃ present, the optical positional range became smaller and hence an increase in the crystallization tendency and a lowering of the v_(d) value with a given n_(d) value of the glass occurred. One attempt to avoid the tendency of the glass to crystallize was to partially replace CaO and La₂ O₃ with BaO and ThO₂, respectively. However, this attempt was not successful because the v_(d) was considerably low and the P_(g),F values were also considerably below the aforementioned normal partial dispersion value. A need therefore has existed for optical glasses having the same optical position as LaC and LaF glasses but with higher partial dispersion P_(g),F than prior known glasses of the same optical position.

OBJECTS OF THE INVENTION

It is therefore a significant object of this invention to provide optical glasses having an improved varying partial dispersion in the optical positional range of lanthanum crown glasses and lanthanum flint glasses.

Another object of this invention is to provide optical glasses having a very good stability with respect to changes in climatic conditions.

Still another object of this invention is the provision of optical glass that can be ground, polished and pressed like ordinary silicate glasses.

It is a further object of this invention to provide optical glasses which exhibit a low susceptibility to staining.

A still further object of this invention is the provision of a composition for the production of optical glasses having an enlarged optical glass range without having the drawback of an appreciable reduction in the P_(g),F value.

BRIEF SUMMARY OF THE INVENTION

Briefly, the invention relates to optical glasses containing barium borosilicate and having a varying partial dispersion P_(g),F [(n_(g) - n_(f))/(n_(F) - n_(C))] in the optical positional range of LaC and LaF glasses wherein the amount of SiO₂ present in the glass satisfies the following condition: ##EQU1## is at least 0.62 and the content of fluorine is at least 7 grams per 100 cc of glass.

DETAILED DESCRIPTION OF THE INVENTION

The compositions of the glasses according to the invention consist essentially of the following materials:

    ______________________________________                                                                        Equivalent                                      Oxide % by wt.   or      Oxides                                                                               %                                               ______________________________________                                         SiO.sub.2                                                                            20-26           26-31                                                                               Si.sub.1/2 O                                                                         42-53        60-66                            B.sub.2 O.sub.3                                                                      2-8.0                B.sub.2/3 O                                                                          5-20                                          BaO   20-38                BaO   9-18                                          MgO   0-6             25-40                                                                               MgO   0-5          10-22                            CaO   0-18                 CaO   0-10                                          SrO   0-18                 SrO   0-10                                          Ba.sub.2 O.sub.3                                                                     20-32                Ba.sub.2/3 O                                                                         10-20                                         Y.sub.2 O.sub.3                                                                      0-25           20-32 Y.sub.2/3 O                                                                          0-20        10-23                             ThO.sub.2                                                                            0-18                 Th.sub.1/2 O                                                                         0-12                                          ______________________________________                                    

The above compositions further comprise at least 2 weight percent or 5 equivalent percent and preferably from 2 to 7 weight or 5 to 20 equivalent percent of F₂ -O. Thus, in a fictitious purely oxidic glass of the above composition range, so much oxygen is to be replaced by 2 fluorine atoms that the increased weight amounts to 2 to 7 grams per 100 grams of oxidic glass. In an analagous manner, F₂ -O is from 5 to 20 equivalent percent which means that 5 to 20 percent of the oxygen are replaced by an equivalent amount of fluorine.

The fluorine content of the glass can be introduced into each compound which is normally employed in the glass-melting art. For example, the fluorine can be introduced by using such compounds as BaF₂, LaF₂, ThF₄, BaSiF₆, etc.

In order to adjust the required n_(d) and v_(d) values, up to 12 equivalent percent of one or more of the following ingredients can be used:

divalent components, e.g., ZnO, PbO and CdO;

tetravalent components, e.g., TiO₂ and ZrO₂ ;

pentavalent components, e.g., Nb₂ O₅ and Ta₂ O₅ ; and

hexavalent components, e.g., WO₃ and MO₃.

The total content of the above-identified highly refracting, weakly or moderately dispersing constituents including La₂ O₃, ThO₂ BaO, SrO, CaO, ZnO, Ta₂ O₅, Nb₂ O₅ and ZrO₂, is to amount to at least 29 equivalent percent or 60 weight percent, Y₂ O₃ can be used as a substitute for La₂ O₃, either is whole or in part. Preferably, up to 25 percent by weight of La₂ O₃ are replaced by Y₂ O₃.

Similarly, in order to adjust the required optical positions and improve the crystallization stability of the optical glasses of this invention having the components BaO, La₂ O₃ and ThO₂, portions of the latter components can be replaced by one or more of the following highly refracting, weakly or moderately dispersing components:

    ______________________________________                                                        weight percent                                                  ______________________________________                                         CaO              0 - 18                                                        SrO              0 - 18                                                        ZnO              0 - 10                                                        Y.sub.2 O.sub.3  0 - 25                                                        ZrO.sub.2        0 -  7                                                        Ta.sub.2 O.sub.5 0 - 12                                                        Nb.sub.2 O.sub.5 0 - 12                                                        ______________________________________                                    

When more strongly dispersing components, e.g., MgO, PbO, CdO, Al₂ O₃, TiO₂ and WO₃, are added to the glasses in order to adjust a required optical position and for crystallization stability, generally up to 8 equivalent percent is utilized.

From 0 to 2 equivalent percent of As₂ O₃, Sb₂ O₃, NaCl, NH₄ NO₃, alkali silicofluorides, etc. can be used as refining agents in the practice of this invention. A preferred refining agent is As₂ O₃ which is preferably used in an amount of 0.3 weight percent of the total composition.

Represented in Tables 1 and 2 are examples of the optical glasses in accordance with the invention. The various ingredients are set forth in terms of percentage by weight as well as equivalent percent.

                                      TABLE 1                                      __________________________________________________________________________     [Compositions in Equivalent Percent]                                                         1   2    3    4    5    6    7    8    9    10                   __________________________________________________________________________     Si.sub.1/2 O  50.8                                                                               50.2 44.2 49.4 50.2 51.6 50.6 50.8 51.3 50.1                 B.sub.2/3 O   14.6                                                                               14.4 19.3 14.3 14.4 14.9 14.5 14.5 14.6 14.2                 MgO           --  --   --   3.1  --   --   --   --   --   --                   CaO           --  --   --   --   --   --   --   --   --   --                   SrO           --  --   --   --   3.5  --   --   --   --   --                   BaO           15.3                                                                               13.4 10.9 14.3 12.9 13.1 14.0 15.4 14.7 13.6                 PbO           --  --   --   --   --   --   --   2.0  3.2  --                   ZnO           --  --   --   --   --   --   --   --   --   5.1                  CaO           --  --   --   --   --   --   --   --   --   --                   La.sub. 2/3 O 16.2                                                                               16.9 18.3 15.9 16.0 15.2 13.8 14.2 13.1 14.0                 Y.sub.2/3 O   --  --   --   --   --   --   --   --   --   --                   Al.sub.2/3 O  --  --   --   --   --   --   --   --   --   --                   Zr.sub.1/2 O  --  --   --   --   --   --   --   --   --   --                   Ti.sub.1/2 O  --  --   --   --   --   --   --   --   --   --                   Tb.sub.1/2 O  3.1 5.1  7.3  3.0  3.0  5.2  7.1  3.1  3.1  3.0                  Nb.sub.2/5 O  --  --   --   --   --   --   --   --   --   --                   Ta.sub.2/5 O  --  --   --   --   --   --   --   --   --   --                   W.sub.1/3 O   --  --   --   --   --   --   --   --   --   --                   total         100.0                                                                              100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                F.sub.2 --O   15.3                                                                               13.4 10.9 15.2 15.5 13.1 14.1 9.3  9.4  9.3                  As.sub.2 O.sub.3 (refining agent)                                                            0.3 0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3                   ##STR1##     0.78                                                                               0.78 0.70 0.77 0.78 0.77 0.78 0.78 0.78 0.78                 highly retractive weakly                                                                     34.6                                                                               35.4 36.5 33.2 35.4 33.5 34.9 32.7 42.2 35.7                 dispersing substances                                                          strongly disp. substances                                                                    0   0    0    3.1  0    0    0    6.8  3.2  0                                  11  12   13   14   15   16   17   18   19                        __________________________________________________________________________     Si.sub.1/2 O  43.7                                                                               51.2 50.2 48.6 43.2 50.3 49.4 50.8 49.6                      B.sub.2/3 O   19.1                                                                               14.4 14.0 13.6 18.8 14.5 14.5 14.5 14.3                      MgO           --  --   --   --   --   --   --   --   --                        CaO           --  --   --   --   --   --   --   --   --                        SrO           --  --   --   --   --   --   --   --   --                        BaO           10.8                                                                               15.6 13.9 13.0 10.6 15.3 14.4 14.4 15.1                      PbO           --  --   --   --   --   --   --   0.3  --                        ZnO           --  --   --   --   --   --   --   0.3  --                        CaO           --  --   --   --   --   --   --   --   --                        La.sub.2/3 O  15.8                                                                               7.5  15.6 15.7 15.6 16.2 16.1 16.2 15.8                      Y.sub.2/3 O   3.4 8.2  --   --   --   --   --   --   --                        Al.sub.2/3 O  --  --   --   --   --   --   --   --   --                        Zr.sub.1/2 O  --  --   6.3  --   --   --   --   0.5  --                        Ti.sub.1/2 O  --  --   --   7.9  --   --   --   --   3.1                       Th.sub.1/2 O  7.2 3.1  --   1.2  7.1  2.1  3.1  3.1  2.1                       Nb.sub.2/5 O  --  --   --   --   4.7  --   2.5  --   --                        Ta.sub.2/5 O  --  --   --   --   --   --   --   --   --                        W.sub.1/3 O   --  --   --   --   --   1.6  --   --   --                        total         100.0                                                                              100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                     F.sub.2 -O    6.2 9.4  9.0  9.0  6.2  15.2 14.4 14.4 15.0                      As.sub.2 O.sub.3 (refining agent)                                                            0.3 0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3                        ##STR2##     0.70                                                                               0.78 0.78 0.78 0.70 0.78 0.77 0.78 0.78                      highly refractive weakly                                                                     37.2                                                                               34.4 35.9 29.9 38.0 33.6 36.1 34.6 33.0                      dispersing substances                                                          strongly disp. substances                                                                    0   0    0    7.9  0    1.6  0    0.3  3.1                                     20  21   22   23   24   25   26   27   28                        __________________________________________________________________________     Si.sub.1/2 O  49.8                                                                               49.4 50.9 43.0 41.4 42.9 41.9 44.6 41.5                      B.sub.2/3 O   13.9                                                                               14.3 14.5 18.8 19.0 18.8 18.3 19.5 18.1                      MgO           --  --   --   --   --   --   --   --   --                        CaO           --  --   --   --   --   --   --   --   --                        SrO           --  --   5.1  --   --   --   --   --   --                        BaO           13.8                                                                               13.2 10.2 10.5 10.7 10.6 10.2 11.0 10.2                      PbO           --  --   --   --   --   0.6  --   --   --                        ZnO           --  --   --   --   --   --   --   --   --                        CaO           --  --   --   --   --   --   --   5.2  --                        La.sub.2/3 O  15.5                                                                               16.0 16.3 17.9 18.1 17.8 13.5 12.3 11.6                      Y.sub.2/3 O   --  --   --   --   --   --   --   --   --                        Al.sub.2/3 O  --  --   --   1.0  --   --   --   --   --                        Zr.sub.1/2 O  5.9 --   --   0.5  --   --   --   --   --                        Ti.sub.1/2 O  --  5.0  --   0.8  --   3.2  --   --   --                        Th.sub.1/2 O  1.1 2.1  3.0  7.1  5.7  6.1  6.9  7.3  6.9                       Nb.sub.2/5 O  --  --   --   --   4.9  --   9.1  --   --                        Ta.sub.2/5 O  --  --   --   --   --   --   --   --   --                        W.sub.1/3 O   --  --   --   --   --   --   --   --   --                        total         100.0                                                                              100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                                                                               100.0                     F.sub.2 --O   8.9 9.2  9.3  10.5 10.7 10.6 6.0  11.0 10.2                      As.sub.2 O.sub.3 (refining agent)                                                            0.3 0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3                        ##STR3##     0.78                                                                               0.77 0.78 0.70 0.68 0.69 0.70 0.70 0.70                      highly refractive weak                                                                       36.3                                                                               31.3 34.6 36.0 39.4 34.5 39.7 30.6 40.4                      dispersing substances                                                          strongly disp. subst.                                                                        0   5.0  0    2.2  0    3.2  0    5.2  0                         __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     TABLE 2 [Compositions in Weight Percent]                                                    1    2    3    4    5    6    7    8    9    10                   __________________________________________________________________________     SiO.sub.2    23.9 23.5 20.8 23.8 23.8 24.9 23.6 23.2 23.2 24.2                 B.sub.2 O.sub.3                                                                             5.3  5.2  7.0  5.3  5.3  5.5  5.2  5.1  5.1  5.3                  MgO          --   --   --   2.0  --   --   --   --   --   --                   CaO          --   --   --        --   --   --   --   --   --                   SrO          --   --   --   --   5.7       --   --   --   --                   BaO          36.7 32.0 26.7 34.9 31.3 2.2  33.4 35.4 33.4 33.0                 PbO          --   --   --   --   --   --   --   6.8  10.8 --                   ZnO          --   --   --   --   --   --   --   --   --   6.6                  CdO          --   --   --   --   '    --   --   --   --   --                   La.sub.2 O.sub.3                                                                            27.7 28.6 31.1 27.7 27.6 26.4 23.1 3.4  21.4 24.5                 Y.sub.2 O.sub.3                                                                             --   --   --   --   --   --   --   --   --   --                   Al.sub.2 O.sub.3                                                                            --   --   --   --   '    --   --   --   --   --                   ZrO.sub.2    --   --   --   --   --   --   --   --   --   --                   TiO.sub.2    --   --   --   --   --   --   --   --   --   --                   ThO.sub.2    6.4  10.5 15.0 6.3  6.3  11.0 14.7 6.1  6.1  6.4                  Nb.sub.2 O.sub.5                                                                            --   --   --   --   --   --   --   --   --   --                   Ta.sub.2 O.sub.5                                                                            --   --   --   --   --   --   --   --   --   --                   WO.sub.3     --   --   --   --   --   --   --   --   --   --                   F.sub.2 -O   5.3  4.6  3.7  5.4  5.3  4.6  4.8  2.9  2.9  3.1                  total        105.3                                                                               104.6                                                                               103.7                                                                               105.4                                                                               105.3                                                                               104.6                                                                               104.8                                                                               102.9                                                                               102.9                                                                               103.1                As.sub.2 O.sub.3 (refining agent)                                                           0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3                  highly refractive weakly                                                       dispersing substances                                                                       0.8  17.3 72.2 68.9 71.9 69.6 71.2 64.9 60.9 70.5                 strongly disp. subst.                                                                       0    0    0    2.0  0    0    0    6.8  10.8 0                    m.sub.d      7.6560                                                                              1.6764                                                                              1.6906                                                                              1.64683                                                                             1.65726                                                                             1.66801                                                                             1.67060                                                                             1.68076                                                                             1.68369                                                                             1.66480              y.sub.d      58.08                                                                               56.32                                                                               55.47                                                                               57.95                                                                               57.36                                                                               56.54                                                                               56.81                                                                               51.22                                                                               49.19                                                                               55.49                n.sub.g -n.sub.6                                                               n.sub.f -n.sub.C                                                                            0.5491                                                                              0.5502                                                                              0.5504                                                                              0.5405                                                                              0.5500                                                                              0.5518                                                                              0.5498                                                                              0.5590                                                                              0.5600                                                                              0.5508               n.sub.g -n.sub.c                                                               n.sub.f -n.sub.C                                                                            1.0067                                                                              1.0102                                                                              1.0104                                                                              1.0091                                                                              1.0109                                                                              1.0119                                                                              1.0098                                                                              1.0216                                                                              1.2059                                                                              1.0110               __________________________________________________________________________                  11   12   13   14   15   16   17   18   19                        __________________________________________________________________________     NiO.sub.2    20.8 25.3 24.9 24.7 20.8 23.8 23.4 23.8 23.8                      B.sub.2 O.sub.3                                                                             7.0  5.5  5.4  5.5  7.0  5.3  5.3  5.3  5.3                       MgO          --   --   --   --   --   --   --   --   --                        CHO          --   --   --   --   --   --   --   --   --                        SiO          --   --   --   --   --   --   --   --   --                        BaO          26.1 39.0 35.2 33.1 26.1 37.0 35.0 34.0 37.1                      PbO          --   --   --   --   --   --   --   1.1  --                        ZnO          --   --   --   --   --   --   --   0.5  --                        CnO          --   --   --   --   --   --   --   --   --                        Na.sub.2 O.sub.3                                                                            27.1 13.3 28.1 28.8 27.1 27.6 27.7 27.6 27.5                      Y.sub.2 O.sub.3                                                                             4.0  10.1 --   --   --   --   --   --   --                        Al.sub.2 O.sub.3                                                                            --   --   --   --   --   --   --   --   --                        ZPO.sub.2    --   --   6.4  --   --   --   --   0.5  --                        TiO.sub.2    --   --   --   5.3  --   --   --   --   2.0                       ThO.sub.2    15.0 6.8  --   2.6  15.0 4.4  6.5  6.3  4.3                       Nb.sub.2 O.sub.5                                                                            --   --   --   --   4.0  --   2.1  --   --                        Ta.sub.2 O.sub.5                                                                            --   --   --   --   --   --   --   --   --                        WO.sub.3     --   --   --   --   --   1.9  --   --   --                        F.sub.2 -O   2.2  3.2  3.3  3.2  2.3  5.3  5.0  5.0  5.3                       total        102.2                                                                               103.2                                                                               103.3                                                                               103.2                                                                               102.3                                                                               105.3                                                                               105.0                                                                               105.0                                                                               105.3                     As.sub.2 O.sub.3 (refining agent)                                              highly refractive weak                                                                      72.2 69.2 69.7 61.5 72.2 69.0 71.3 69.8 68.9                      dispersing substances                                                          strongly disp. subst.                                                                       0    0    0    5.3  0    1.9  0    1.1  2.0                       h.sub.d      1.70571                                                                             1.65876                                                                             1.67777                                                                             1.69932                                                                             1.21580                                                                             1.66717                                                                             1.66350                                                                             1.65717                                                                             1.67727                   v.sub.d      53.87                                                                               56.53                                                                               53.54                                                                               47.06                                                                               50.41                                                                               55.33                                                                               54.53                                                                               56.84                                                                               52.44                     D.sub.g -D.sub.f                                                                            0.5512                                                                              0.5500                                                                              0.5521                                                                              0.5666                                                                              0.5564                                                                              0.5529                                                                              0.5531                                                                              0.5500                                                                              0.5572                    N.sub.f -D.sub.c                                                               N.sub.g -N.sub.g                                                               N.sub.f -N.sub.c                                                                            1.0112                                                                              4.0099                                                                              1.0126                                                                              1.0314                                                                              1.0189                                                                              1.0137                                                                              1.0139                                                                              1.0298                                                                              1.0192                    __________________________________________________________________________                  20   21   22   23   24   25   26   27   28   29                   __________________________________________________________________________     SiO.sub.2    24.4 24.5 24.9 20.4 19.7 20.3 20.6 20.7 20.7 21.0                 B.sub.2 O.sub.3                                                                             5.3  5.5  5.5  6.9  7.0  6.9  6.9  7.0  7.0  6.1                  MgO          --   --   --   --   --   --   --   --   --   --                   C.sub.2 O    --   --   --   --   --   --   --   --   --   --                   SrO          --   --   8.6  --   --   --   --   --   --   --                   BaO          34.5 33.4 5.5  25.4 26.1 5.6  25.8 26.1 6.1  26.8                 PbO          --   --   --   --   --   --   --   --   --   --                   ZnO          --   --   --   --   --   --   --   --   --   --                   CdO          --   --        --   --   --   --   10.4 --   --                   La.sub.2 O.sub.3                                                                            27.5 28.7 28.9 30.5 31.1 30.5 23.9 20.8 20.8 30.4                 Y.sub.2 O.sub.3                                                                             --   --   --   --   --   --   --   --   --   --                   Al.sub.2 O.sub.3                                                                            --   --   --   0.5  --   --   --   --   --   --                   ZrO.sub.2    6.0  --   --   0.5  --   --   --   --   --   --                   TiO.sub.2    --   3.3  --   0.5  --   2.0  --   --   --   --                   ThO.sub.2    2.3  4.6  6.6  14.8 11.9 12.7 14.9 15.0 15.0 0.2                  Nb.sub.2 O.sub.5                                                                            --   --   --   --   4.2  --   7.9  --   10.14                                                                               --                   Ta.sub.2 O.sub.5                                                                            --   --   --   --   --   --   --   --   --   5.5                  WO.sub.3     --   --   --   0.5  --        --   --   --   --                   F.sub.2 -O   3.2  3.3  3.2  3.6  3.7  3.7  2.2  3.7  3.7  5.6                  total        103.2                                                                               103.3                                                                               103.2                                                                               103.6                                                                               103.7                                                                               103.7                                                                               102.2                                                                               103.7                                                                               103.7                                                                               05.6                 As.sub.2 O.sub.3 (refining agent)                                                           0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3  0.3                  highly refractive weakly                                                       dispersing substances                                                                       70.3 66.7 69.6 71.2 73.3 68.8 72.5 61.9 72.3 72.9                 strongly disp. substances                                                                   0    3.3  0    1.5  0    4.0  0    10.4 0    0                    n.sub.d      1.67621                                                                             1.68671                                                                             1.66573                                                                             1.69690                                                                             1.71202                                                                             1.70668                                                                             1.73292                                                                             1.70976                                                                             1.74243                                                                             1.68816              v.sub.d      53.92                                                                               50.72                                                                               56.42                                                                               53.61                                                                               50.60                                                                               50.05                                                                               46.71                                                                               51.66                                                                               44.58                                                                               53.76                n.sub.g -n.sub.F                                                                            0.5513                                                                              0.5607                                                                              0.5501                                                                              0.5530                                                                              0.5571                                                                              0.559                                                                               0.5620                                                                              0.5546                                                                              0.5656                                                                              0.5531               n.sub.g -n.sub.e                                                               n.sub.F -n.sub.C                                                                            1.0120                                                                              1.0238                                                                              1.0102                                                                              1.0139                                                                              1.0192                                                                              1.0227                                                                              1.0255                                                                              1.0160                                                                              1.0302                                                                              1.0142               __________________________________________________________________________

Reference is also made to the attached figures. FIG. 1 shows the optical positional range of the glasses in accordance with the invention. FIG. 2 shows the dependence of (n_(g) - n_(f))/(n_(F) - n_(c)) = P_(g),F on (n_(d) -1)/(n_(F) -n_(C)) = v_(d) of known glasses and of the glasses according to the invention. In FIG. 2, both glasses of this invention as well as glasses of the prior art have the same optical position, but the glasses of this invention are shown to exhibit higher partial dispersion P_(g),F than the prior art glasses. In these figures, the crosses indicate the glasses according to the inventon. The other markings correspond to commercial LaC and LaF glasses, which are to be found in the 1966 Schott catalogue and 1968 Min catalogue with the indicated numberings.

ILLUSTRATIVE EXAMPLES

The following examples are given by way of illustration of this invention only, and should not be construed as being in any way limiting upon the scope thereof. All percentages are by weight, unless specified to the contrary.

In the production of glass according to each of these examples, the following procedure was used.

The initial materials are well-mixed. The batch is melted at 1460° to 1480° C. in a platinum crucible and refined for two hours at 1520° C. Thereafter the temperature is lowered and stirring takes place from 1420° to 1030° C. The puring takes place at about 980° C. into a preheated casting mold. The reproducibility of the optical values is guaranteed by a melting assembly which is closed as tightly as possible, particularly so that the vaporization of the fluorine can be kept under control and influence the properties of the final melt product.

EXAMPLE 1

The following initial materials were used:

    ______________________________________                                                        Weighed quantity for 4.6                                                       kg. melt in grams                                               ______________________________________                                         SiO.sub.2        921.1                                                         H.sub.3 BO.sub.3 549.6                                                         BaF.sub.2        1329.1                                                        La.sub.2 O.sub.3 1395.7                                                        ThO.sub.2        668.3                                                         As.sub.2 O.sub.3 13.8                                                          ______________________________________                                    

thus producing a charge for a 4.6 kg. melt having the following proportions:

    ______________________________________                                                      Percent by Weight                                                 ______________________________________                                         SiO.sub.2       20.75                                                          B.sub.2 O.sub.3                                                                                7.00                                                           BaO             26.08                                                          La.sub.2 O.sub.3                                                                               31.12                                                          ThO.sub.2       15.05                                                          Total Oxides:  100.00 percent                                                  F.sub.2 -O      3.74 (increase in Weight due to                                               oxygen replaced by fluorine)                                    As.sub.2 O.sub.3 (refining agent)                                                              0.30                                                           ______________________________________                                    

EXAMPLE 2

The following initial materials were used:

    ______________________________________                                                        Weighed quantity for 4.6                                                       kg. melt in grams                                               ______________________________________                                         SiO.sub.2        1133.6                                                        H.sub.3 BO.sub.3 449.4                                                         BaCO.sub.3       308.4                                                         Ba(NO.sub.3).sub.2                                                                              394.5                                                         BaF.sub.2        1228.2                                                        La.sub.2 O.sub.3 1338.2                                                        TiO.sub.2        244.8                                                         ThO.sub.2        119.8                                                         As.sub.2 O.sub.3 13.8                                                          ______________________________________                                    

thus producing a charge for a 4.6 kg. melt having the following proportions:

    ______________________________________                                                        Percent by Weight                                               ______________________________________                                         SiO.sub.2        24.6                                                          B.sub.2 O.sub.3  5.3                                                           BaO              33.5                                                          La.sub.2 O.sub.3 28.8                                                          TiO.sub.2        5.2                                                           ThO.sub.2        2.6                                                           Total Oxides:    100.0                                                         F.sub.2 -O       3.3                                                           Overall Total:   103.3                                                         As.sub.2 O.sub.3 (refining agent):                                                              0.3                                                           ______________________________________                                    

Having now discussed in considerable detail illustrative and preferred embodiments of the invention, it should be apparent that the objects set forth at the outset of this specification have been satisfied. 

Accordingly, what is claimed is:
 1. Optical glasses containing barium borosilicate having a varying partial dispersion P_(g),F = (n_(g) - n_(f))/(n_(F) - n_(C)) in the optical positional range of lanthanum crown and lanthanum flint glasses having an index of refraction of about 1.642 to 1.742 and v_(d) of about 44.0 to 58.0 and wherein the amount of SiO₂ present in the glass satisfies the following condition: ##EQU2## is at least 0.62 and the content of fluorine in said glass is at least 7 grams per 100 cc. of said glass consisting essentially of:

    ______________________________________                                                          weight percent                                                ______________________________________                                         SiO.sub.2          20 to 26                                                    B.sub.2 O.sub.3    3 to 8                                                      BaO                20 to 38                                                    MgO                0 to 6                                                      CaO                 0 to 18                                                    SrO                 0 to 18                                                    La.sub.2 O.sub.3   20 to 32                                                    Y.sub.2 O.sub.3     0 to 25                                                    ThO.sub.2           0 to 18                                                    ______________________________________                                    

and up to 12 equivalent percent of one or more of the following ingredients to adjust the required n_(d) and v_(d) values: ZnO, PbO, CdO, TiO₂, ZrO₂, Nb₂ O₅, Ta₂ O₅, WO₃, MO₃ and mixtures thereof.
 2. Optical glass according to claim 1 consisting essentially of:

    ______________________________________                                                        weight percent                                                  ______________________________________                                         SiO.sub.2 and B.sub.2 O.sub.3                                                                   26 to 31                                                      BaO + MgO + CaO + SrO                                                                           25 to 40                                                      La.sub.2 O.sub.3 + Y.sub.2 O.sub.3 + ThO.sub.2                                                  20 to 32                                                      ______________________________________                                    


3. Optical glass of claim 1 comprising 60 percent by weight of highly refracting, weakly or moderately dispersing materials selected from the group consisting of La₂ O₃, ThO₂, ZrO₂, BaO, SrO, CaO, ZnO, Ta₂ O₅, Nb₂ O₅ and mixtures thereof.
 4. Optical glass of claim 3 wherein Y₂ O₃ is added to the composition to substitute an equal amount of La₂ O₃.
 5. Optical glass of claim 4 wherein up to 25 weight percent of said La₂ O₃ is substituted with Y₂ O₃.
 6. Optical glass of claim 5 further containing a strong dispersing material selected from the group consisting of MgO, PbO, CdO, Al₂ O₃, TiO₂, WO₃ and mixtures thereof, in an amount sufficient to adjust the required optical position and crystallization stability of said glass.
 7. Optical glass of claim 3 further containing a strong dispersing material selected from the group consisting of MgO, PbO, CdO, Al₂ O₃, TiO₂, WO₃ and mixtures thereof, in an amount sufficient to adjust the required optical position and crystallization stability of said glass.
 8. Optical glass according to claim 1 comprising:

    ______________________________________                                                        weight percent                                                  ______________________________________                                         SiO.sub.2        20 to 26                                                      B.sub.2 O.sub.3  2 to 8                                                        BaO              20 to 38                                                      La.sub.2 O.sub.3 20 to 32                                                      ThO.sub.2         0 to 18                                                      F.sub.2 -O       2 to 7                                                        ______________________________________                                    

and wherein the total amount of SiO₂ and B₂ O₃ present in the composition is between 26 and 31 weight percent.
 9. Optical glass of claim 1 further containing the following strongly dispersing ingredients:

    ______________________________________                                                        weight percent                                                  ______________________________________                                         CdO              0 to 8                                                        PbO               0 to 10                                                      Al.sub.2 O.sub.3 0 to 7                                                        TiO.sub.2        0 to 8                                                        WO.sub.3         0 to 7                                                        ______________________________________                                    

wherein the total amount of said ingredients present in said glass is no greater than 8 equivalent percent.
 10. Optical glass of claim 1 comprising the following materials:

    ______________________________________                                                        weight percent                                                  ______________________________________                                         SiO.sub.2        20.75                                                         B.sub.2 O.sub.3   7.00                                                         BaO              26.08                                                         La.sub.2 O.sub.3 31.12                                                         ThO.sub.2        15.05                                                         ______________________________________                                    

and 3.74 weight percent of F₂ -O based upon the total weight of oxides present in said glass.
 11. Optical glass of claim 1 comprising the following materials:

    ______________________________________                                                        weight percent                                                  ______________________________________                                         SlO.sub.2        24.6                                                          B.sub.2 O.sub.3  5.3                                                           BaO              33.5                                                          La.sub.2 O.sub.3 28.8                                                          TiO.sub.2        5.2                                                           ThO.sub.2        2.6                                                           ______________________________________                                    

and 3.3 weight percent of F₂ -O based upon the total weight of oxides present in said glass.
 12. Optical glass of claim 1 containing 2 to 7 weight percent of F₂ -O based upon the total weight of oxides present in said glass. 